This invention is a particular design of a timed contact manually operated switch. By "timed contact switch" is meant a switch which when actuated by a user, retains its actuated condition for a predetermined time period. Certain types of such switches incorporate mechanical with a timing element which actuates the contacts for the time period. Of course, such a switch need not be one which, when actuated has conduction between terminals of the switch for the period of time, but may be one for which conduction is interrupted during the time period. These switches have use in various applications, such as controlling power to defroster apparatus, lights, etc.
There have been any number of different designs for these timed contact switches. Some use a bimetal strip which is slowly heated by current passing through a resistance element within the unit, and which breaks (changes) the contact when a certain temperature is reached. Others use a slowly operating fluid dashpot in combination with a mechanical spring which after a period of time restores the switch to its normal condition. There are certain applications however, where high reliability is necessary and where the unit's "on" time period must be independent of temperature and pressure. These may arise in safety critical operations such as in aircraft, furnace controls, etc.
Valve control mechanisms having some resemblance to the apparatus of this invention have been used for controlling liquid dispensing on a timed basis in, for example, vending machines. Indeed, these devices constitute the best art of which applicants are aware. The resemblance arises from the use in both of a winding to which flow of power is controlled by a timing circuit.